Optical switching apparatus

ABSTRACT

An optical matrix switch station ( 1 ) is shown mounting a plurality of optical switch units ( 15, 17 ), each of which includes a mirror ( 29 ), moveable in two axes, for purpose of switching light beams from one optical fiber to another. A mirror assembly ( 41 ) is formed from a single body of silicon and comprises a frame portion ( 43 ), gimbals ( 45 ), mirror portion ( 47 ), and related hinges ( 55 ). Magnets ( 53, 54 ) and air coils ( 89 ) are utilized to position the central mirror surface ( 29 ) to a selected orientation. The moveable mirror and associated magnets along with control LED&#39;s ( 71 ) are hermetically packaged in a header ( 81 ) and mounted with the air coils on mounting bracket ( 85 ) to form a micromirror assembly package ( 99 ) mounted in each optical switch unit.

RELATED APPLICATIONS

Benefit is claimed from Provisional Application No. 60/088,239. filedJun. 5, 1998.

FIELD OF INVENTION

This invention relates generally to optical switching and moreparticularly to non-electrical switching of laser communication signals.

BACKGROUND OF THE INVENTION

In recent years optical fibers have come into wide spread use in a widevariety of applications in which optical signals are transmitted alongsuch fibers and are switched from one fiber to another by means of anoptical switch. Conventional optical switches generally include fiberpositioning means, alignment signal emitter means and interconnectedcomputer control means. A fiber positioning means is provided near theend of each fiber to selectively point the and of a given fiber in onefiber group toward the end of a given fiber in another fiber group forswitched optical transmission therebetween. An alignment signal emittermeans is provided near an end of and in predetermined spacedrelationship to the end of each fiber to emit an alignment signal forreceipt and use in controlling the fiber positioning means when aligningthe ends of selected fibers in the fiber groups for switched opticaltransmission therebetween, for example as shown in U.S. Pat. Nos.4,512,036 and 5,177,348. This approach requires considerable complexityand duplication of alignment means for each alignable fiber. It would bevery desirable to reduce this complexity and duplication and to increasespeed of switching, reliability, as well as to reduce cost inimplementation.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an optical switch thatovercomes the limitations of the above noted prior art. Another objectof the inventions is to provide an optical switching unit which isrelatively low in cost, has high speed and is reliable in operation.Briefly in accordance of the invention, an improved optical lighttransmission switch employs a microelectromechanical (hereinafter MEM)movable mirror assembly with associated electromagnet coils mounted in apackage and preferably including control LED's with both drive and LEDsignals being supplied through a wiring harness. The following describedpreferred embodiments relate to a hermetic package using inorganicmaterials in order to provide extended life, however, units can be madewhich include organic materials for other shorter life applications.

The package comprises an LED lead frame of suitable material such asceramic, which mounts LED's used by the control system to aim themovable mirror as well as circuitry to electrically connect the LED's totheir package terminations. As will be discussed below, the LED'sprovide signals for controlling the position of the movable mirror sothat any two mirrors in an array can be positioned to reflect a lightbeam precisely at each other so that the light beam is focused entirelyon the reflective surface of the mirrors and in that way no energy ofthe beam is lost in the reflection process of the switched connection.The LED's are die and wire bonded to the lead frame using conventionaltechniques. The LED's are located so that lines drawn through diagnonalpairs would pass through a selected location on the lead frame which isreferenced the movable mirror. A mirror assembly, described below, isattached to the lead frame so that the center of the mirror portioncoincides with the selected location on the lead frame in order toaccurately locate the mirror relative to one another for proper controlof mirror movement. The mirror assembly and lead frame are mounted in aheader of suitable material, such as ceramic which, along with drivingmeans and a wiring harness, are in turn mounted on a bracket. Thepackage is received in a housing in which an optical fiber is receivedand in which another mirror is disposed in alignment with the fiber forreflecting an optical signal from the fiber to the movable mirror.

MEM micromirrors are presently used to build digital micromirror display(DMD) devices where the mirrors rotate about a single axis by anelectrostatic drive. The mirror of the present invention provides twoaxes of motion and is preferably driven magnetically. The micromirror ispreferably made from a single piece of crystal material such as siliconand has three portions connected by two sets of hinges. An inner portionforms the mirror. One of the hinge pairs, one hinge on each of twoopposite sides of the mirror portion, ties the mirror portion and themiddle gimbals portion, which surrounds the mirror portion. This allowsthe mirror portion to rotate about the gimbals portion, providing thefirst axis of rotation. The second set of hinges ties the gimbalsportion and the frame portion, one hinge on each of two opposite sideson a line disposed, 90 degrees relative to a line drawn through thefirst set of hinges. This allows the gimbals portion, which carries themirror, to rotate about the frame portion, providing a second axis ofrotation.

Two pair magnets, one for each axis of rotation, are used to move themirror portion and are mounted on one face of the single piece to form amirror assembly. The first pair of magnets are attached by suitablemeans to the mirror portion of the mirror assembly, one on each of twoopposite sides of a line, 90 degrees relative to a line through themirror/gimbals portions set of hinges. When magnetically stimulated, themirror portion rotates about the mirror/gimbals portions set of hinges,providing the first axis of motion. The second pair of magnets aresuitably attached to the gimbals portion of the mirror assembly, one oneach of two opposite sides of a line, 90 degrees relative to a linedrawn through the gimbals/frame portions set of hinges. Whenmagnetically stimulated, the mirror and gimbals portions rotate aboutthe second set of axis, to providing the second axis of rotation.

According to a feature of the invention, an additional magnet isprovided at each magnet location, with the poles in opposingrelationship to each other and disposed on the opposite face of mirrorassembly to balance the weight of the magnets relative to the hingecenterlines of the mirror assembly, eliminating undesirable oscillationsunder external shock or other conditions.

According to a modified embodiment, a single magnet can be utilizedlocated in the center of the mirror portion, on the face opposing thesurface serving as the mirror.

According to another feature of the invention, motion stops, disposed ina plane described by the two axes of rotation, are added to the mirrorassembly at each hinge location to limit motion and thereby preventfailure of the hinge. Tabs are preferably formed in the plane describedby the two axes of rotation, extending from the mirror portion to thegimbals portion and from the gimbals portion to the frame portion, toprevent rotation during initial manufacture. Sometime prior to finalassembly, laser or other suitable cutting means severs the tabs,preferably perpendicular to each respective axis of the hinges, to allowfree rotation.

In order to obtain extended operation without degradation, the mirrorassembly is preferably hermetically assembled into a cavity in thepackage to lock out moisture and allow the provision of a benignatmosphere for micromirror operation. The cavity can be filled withselected gases to provide improved heat transfer and, if desired,exclude oxygen or other gases that would adversely affect themicromirror over time. The hermetic package comprises the header inwhich the cavity is formed and which includes sealed pins for electricalLED connection pins. A peripheral seat surface on the header extendingaround the cavity is coated with indium or suitable non-organic sealmaterials, for later attachment of a window over the cavity. The use ofindium allows the seal to be made at room temperature to avoid sealtemperature induced stresses and window distortions. Indium or othernon-organic attach materials are used exclusively to assembly all itemswithin the body cavity of the hermetic package, avoiding any unwantedlong term organic out gassing or other similar problems.

According to another feature, the window is tilted at a slight angle,such as 6 degrees, to deflect unwanted stray light away from the desiredoptical path.

The lead frame assembly described above, containing LED's and the mirrorassembly, is placed in and attached to the body on a platform within thecavity. The tabs preventing rotation of the mirror and gimbals portionsduring assembly may now be released as described above. The body cavityis sealed with a glass window that preferably has been treated withanti-reflective coatings.

An air coil drive assembly is used and preferably employs a push andpull arrangement for driving the mirror magnets to rotate the mirrorportion to the desired orientation in its two axes. Four air coilassemblies, comprising copper wire coiled on a bobbin, are attached to amounting bracket, trapping a flex circuit harness and are aligned withthe mirror assembly. The air coil leads are soldered to the flex circuitharness to allow system electrical control of the air coils and theirpush pull arrangement to drive the mirror assembly. The air coil bobbinsare made of aluminum or other eddy current generating material, andsufficient amounts of aluminum are provided at the top and bottom of thebobbins to allow eddy current dampening of the movable portions of themirror assembly, to prevent unwanted oscillations. In order to preventoverheating and loss of mirror position control, the air coil bobbinsare made of high heat transfer material, such as aluminum, and thebobbins are massive relative to the air coils. The mounting bracket ismassive relative to the bobbins and is also made of a high heat transfermaterial, such as aluminum. The bracket is in intimate contact with theoptical unit housing, which in turn is in intimate contact with theultimate heat sinking of the customers system.

According to yet another feature, the air coil bobbins trap the flexcircuit harness to the bracket when the air coil bobbins are attached tothe bracket to facilitate later location and assembly of the flexcircuit to the bracket. The LED pins of the header assembly are solderedto the appropriate pads on the flex circuit harness. The micromirror canfully be tested at this point. The header assembly is then rotated andaligned with the mounting bracket and joined by fixing the headerassembly to the mounting bracket. The open area around the air coils isthen potted with heat conductive material to ensure optimum assemblyrigidity and improved heat transfer.

Other objects and advantages of the present invention will be apparentfrom the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and furtheradvantages thereof, reference is now made to the following detaileddescription of the preferred embodiments taken in conjunction with thedrawings in which:

FIG. 1 is a schematic view of an optical switching station showing twooptical switching units;

FIG. 2 is a schematic view of one of the optical switching units shownin FIG. 1;

FIG. 3 is a plan view of a mirror assembly used in the FIG. 2 switchunit;

FIG. 3 a is a cross sectional view taken on line A-A of FIG. 3;

FIG. 3 b is a view similar to FIG. 3 a but showing rotation of themirror portion of the mirror assembly;

FIG. 3 c is a cross sectional view taken on line B-B of FIG. 1;

FIG. 3 d is a view similar to FIG. 3 c but showing rotations of thegimbals portion of the mirror assembly;

FIG. 4 is an enlarged cross sectional plan view taken on line E-E of 3 ashowing a hinge and an in-plane motion stop;

FIG. 5 is an enlarged, broken away portion of FIG. 4 showing a portionof the in-plane stop;

FIG. 6 is a cross sectional plan view taken on line E-E of FIG. 3 a,showing a hinge with an optional lock down tab to stop rotation usedduring manufacture;

FIG. 6 a is a view similar to FIG. 6 showing the lock down tab severedto allow rotation;

FIG. 7 is a top plan view of an optical switch package made inaccordance with the invention;

FIG. 7 a is a cross sectional view taken on line C-C of FIG. 7;

FIG. 7 b is a view similar to FIG. 7 showing rotation of the mirrorportion of the mirror assembly;

FIG. 7 c is a cross sectional view taken on line D-D of FIG. 7;

FIG. 7 d is a view similar to FIG. 7 c but showing rotation of thegimbals portion of the mirror assembly;

FIG. 8 is an exploded view of a cross sectional, broken away portion ofthe bottom wall of the housing of an optical switching unit package andthe mounting bracket;

FIG. 9 is a top plan view of a modified embodiment of an optical switchunit with certain parts removed for purposes of illustration;

FIG. 9 a is a cross sectional view of the top portion of an opticalswitch unit taken on line F-F of FIG. 9; and

FIG. 9 b is a view similar to FIG. 9 a but showing rotation of themirror portion of the modified mirror assembly.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows the layout of a matrix optical switch station comprising aplurality of parallelly extending optical switch units 5 and 15, twobeing shown for purposes of illustration, but any number can be providedas desired. These switch units are mounted in a frame 3 such that theyare aligned with optical switch mirror 11 fixedly mounted in housing 1.An end portion of fiber optics cable 17 is mounted in a selected fixedposition within housing 15 and fiber optics cable 7 is similarly affixedinto the housing of optical switch 5. A light signal 13 is transmittedin cable 17 and is directed by optical switch unit 15, by reflectinglight signal 13 from optical switch mirror 11 to another selectedoptical switch unit, such as optical switch 5, which directs lightsignal 13 into cable 7.

A light beam controlled by a single movable mirror will enter varioustarget positions with an angle of incidence that varies with the targetposition of the beam. The use of two movable mirrors in the systemallows a beam of light emitted on a longitudinal axis to be directed atany angle by the first movable mirror and exit the second movable mirroron a defined longitudinal axis that is invariant with changes in theincident angle of the beam. By maintaining a defined axis for the lightbeam, the use of two movable mirrors acts to simplify any tens used foran optical switch.

The light signal is optimized to minimize transmission losses by theoptical units. As seen in FIG. 2, light beam 13 carried by optical cable17 is reflected by a fixed mirror 25 mounted within optical switch 15 toa moveable mirror 29, shown in a solid line in its middle or neutralunpowered position. Mirror 29 is moveable between two opposite extremes,29′, 29″, with light beam 13 correspondingly reflected to 13′, 13″,respectively.

The first movable mirror 29 selects the target position for creating anoptical path. Movable mirror 29 can select any one of a plurality ofoptical switch units to create an optical connection by directing thelight beam 13 to the movable mirror on the second unit. Light beam 13when it is targeted on the second movable mirror is again reflected atan angle that is based on the incident angle of the beam. By operatingthe second movable mirror the incident angle of the beam can be changedsuch that the light is reflected on the longitudinal axis of the secondoptical switch unit.

LED's mounted in an array adjacent a first movable mirror 29, asdisclosed below, provide radiation which is detected by detector 16.Radiation from the LED's in the array associated with the first movablemirror is received in a radiation guide of another, selected fiber andindividually measured by control 100 (FIG. 7 a). The position of theassociated movable mirror of the selected fiber is adjusted untilradiation received from each LED from the first mirror is substantiallyequal, as described in relation to moving fiber ends in U.S. Pat. No.5,177,348, supra.

Although the movement of the mirror shown in FIG. 2 illustrates movementin one plane, mirror movement in a second plane is also included in theoperation of the switch and will be described below.

Mirror assembly 41, FIG. 3, is preferably formed from one piece ofcrystal material such as silicon, etched to provide an outer frameportion 43 forming an opening in which an intermediate annular gimbalsportion 45 is attached at opposing hinge locations 55 along first axis31. An inner, centrally disposed mirror portion 47, having a mirror 29centrally located thereon, is attached to gimbals portion 45 at hingeportions 55 on a second axis 35, 90 degrees from the first axis. Mirror29 is suitably polished on its upper surface to provide specular surfaceand, preferably, is similarly polished on its lower surface as well, inorder to prevent stresses in the material which could otherwise cause acertain warpage due to the thinness of the sheet material, e.g., on theorder of 100 microns.

A first pair of permanent magnets 53 is mounted on gimbals portion 45along the second axis and a second pair of permanent magnets 53 ismounted on extensions 51, which extend outwardly from mirror portion 47along the first axis. In order to symmetrically distribute mass aboutthe two axes of rotation to thereby prevent oscillation under shock andvibration, each permanent magnet 53 preferably comprises a set of anupper magnet 53 a mounted on the top surface of the mirror assembly 41using conventional attachment techniques such as indium bonding, and analigned lower magnet 53 b similarly attached to the lower surface of themirror assembly as shown in FIGS. 3 a-3 d. The magnets of each set arearranged serially such as the north/south pole arrangement indicated inFIG. 3 c. There are several possible arrangements of the four sets ofmagnets which may be used, such as all like poles up, or two sets oflike poles up, two sets of like poles down, or three sets of like polesup, one set of like pole down, depending upon magnetic characteristicsdesired.

By mounting gimbals portion 45 to frame portion 43 by means of hinges55, motion of the gimbals portion 45 about the first axis 31 is providedand by mounting mirror portion 47 to gimbals portion 45 via hinges 55,motion of the mirror portion relative to the gimbals portion is obtainedabout the second axis 35, thereby allowing independent, selectedmovement of the mirror portion 47 along two different axes.

The middle or neutral position of mirror assembly 41 is shown in FIG. 3a, which is a section taken through the assembly along line A-A of FIG.3. Rotation of mirror portion 47 about axis 35 independent of gimbalsportion 45 and/or frame portion 43 is shown in FIG. 3 b as indicated bythe arrow. FIG. 3 c shows the middle position of the mirror assembly 41,similar to that shown in FIG. 3 a, but taken along line B-B of FIG. 3.Rotation off the gimbals portion 45 and mirror portion 47 about axis 31independent of frame portion 43 is shown in FIG. 3 d as indicated by thearrow. The above independent rotation of mirror 29 of mirror portion 47about the two axes allows direction of light beam 13 as needed by theoptical switch units.

In order to protect hinges 55 from in-plane shock during handling andshipping, stops 57 are provided according to an optional feature of theinvention as best shown in FIGS. 4 and 5, which are enlarged sectionalviews taken on line E-E of FIG. 3 a. At this point it should be notedthat the mirror assembly is on the order of 100 microns thick, whereashinge 55 is on the order of 10 microns wide, thereby providing robuststrength in directions normal to the surface of the assembly. In orderto provide protection against excess in-plane motion 90 degrees to theaxis of the hinge, i.e., axis 31, cooperating surfaces 61 on gimbalsportion 45 and 63 on frame portion 43 are formed on either side of eachhinge 55 and extend generally parallel to axis 31. Surfaces 61 and 63are spaced apart a selected distance such as 10 microns by way ofexample. In order to provide less in-plane motion, projection 65,extending from surface 63 towards surface 61, is formed to any selecteddistance such as 5 microns. It will be understood that such projectioncould be provided on surface 61 instead of 63 if desired. Similar stopsare provided on the mirror and gimbals portions to provide protectionagainst in-plane motion of hinges 55 relative to axis 35.

According to another optional feature of the invention, lock down tabsassociated with each hinge are provided. As seen in FIG. 6, an exampleshowing one such hinge 55, bridge portion 67 extends from gimbalsportion 45 to frame portion 43 and locks the two portions togetherisolating hinge 55 from all normal manufacturing stresses. At theappropriate manufacturing step, the bridge portion 67 is cut providinggap 69 as shown in FIG. 6 a, which allows normal rotation of gimbalsportion 45 relative to frame portion 43 about the hinge 55. Thisprovides suitable stress protection for all hinges and significantlyimproves manufacturing yields.

With reference to FIG. 3, extensions 51 are preferably provided withlaterally extending tabs 51 a which can be used to clamp down the mirrorportion during assembly to thereby provide additional stress protection.

The movable mirror assembly 41 is received in a cavity 81 a of a header81 which forms part of the mirror assembly package shown in FIGS. 7-7 d.Header 81 is formed of any suitable material, such as ceramic in thecase of a hermetic package and plastic where hermeticity is notrequired, and hat a circumferentially extending shelf 81 b formed withincavity 81 a on which frame portion 43 of mirror assembly 41 is received.Bottom wall 81 c is spaced from shelf 81 b to provide clearance formovement of gimbals portion 45 and mirror portion 47. Recesses 81 d areformed in bottom wall 81 c aligned with each set of magnets 53 toprovide motion clearance for lower magnets 53 b. The size of the openingof recesses 81 d is maintained as small as possible, allowing suitablemotion of the magnets, to facilitate making wall 81 e as thin aspracticable, for example 125 microns.

The magnet drive for the magnets comprise four air coils 89 (two shownin FIGS. 7 c-7 d) each wound on a bobbin in turn mounted on mountingbracket 85 and aligned with respective recesses 81 d and magnets 53. Thebobbin and bracket are made of suitable material for good heat transfer,magnetic dampening, and strength such as aluminum. The air coils arewound using high electrical conductivity materials such as copper. Thebobbin has an air coil disposed proximate to top end 89 a of bobbin 89such that the air coil is as close to magnets 53 as possible, forexample, 200 microns, to provide full mirror rotation using minimumpower.

An electrical wiring harness 87 is provided for required electricalconnections to the micromirror assembly package 99 and comprises anelongated flex circuit 87 mounting a connector 95 at one end thereof forconnection to a control system (indicated at 100, FIG. 7 a). An opening87 b is formed at an opposite end which receives therein bobbins 89.Coil leads 97 are attached to appropriate traces on the flax circuit asshown in 7 c-7 d. A plurality of diode pins 79 are mounted in boresprovided in shelf 81 b and extend above and below the shelf. The upperportion of the diode pins are connected by leads 77 to respectiveconductive pads 75 a-75 h (see FIG. 7) and on the lower end areconnected to respective traces on electrical harness 87. LED's 71 a-71 dare assembled to board 75 in according to conventional semiconductortechniques and are powered by the traces on the harness discussed above.The LED's 71 a-71 d are positioned so that they can be used to directthe light beam 13 using the optic unit's sensing control system 100. Thecontrol system can be similar to that described in U.S. Pat. No.5,177,348, as discussed above.

Once the electrical connections are made to the diode pins 79, window 83is attached to the open side of header 81, closing cavity 81 a. Theclosing of cavity 81 a can be made to be a hermetic seal by using knowntechniques such as employing indium as the window seal material andglass sealing or the like sealing of the diode pins 79 to the header 81.If desired, a protective atmosphere such as nitrogen can be trappedwithin the cavity. The window is of suitable material to allowtransmission of light signal 13 with minimum losses and is preferablytilted approximately 6 degrees relative to the plane in which mirrorassembly lies, to deflect unwanted stray light. In this respect, thespacing between gimbals portion 45 and mirror portion 47 is maintainedsufficiently large to avoid unwanted stray light.

After the electrical connections are made between diode pins 79 andharness 87 completing all electrical connections, header 81 with all ofits internal components described above, are aligned with mountingbracket 85 and its components and potted in place with thermallyconductive, strong potting material 93 to complete the micromirrorassembly package 99.

With particular reference to FIG. 8, micromirror assembly package 99 isprecisely mounted and orientated in optical switch unit 15 utilizingcooperating registration surfaces of mounting bracket 85 and a portionof wall 16 of switch unit 15. First opposing tapered surfaces 107 and105 forming a somewhat convex configuration on mounting bracket 85cooperate with respective second opposing tapered surfaces 103 and 101,forming a somewhat concave, or cradle configuration, respectively, onbottom wall 16 of the switch unit. Mounting bolt 113 is received throughbore 111 in bracket 85 and threaded bore 16 a in the cradle in bottomwall 16 to secure micromirror assembly package 99 within optical switchunit 15. The cooperating opposed surfaces provide a precise registrationin two planes while bolt 113 and its corresponding bore 111 in bracket85 and threaded bore 16 a in wall 16 provides registration in a thirdplane.

An alternate embodiment is shown in FIG. 9 in which a single permanentmagnet 54 is centrally located on the lower side of the mirror portion47. Air coils 89 a-89 d are shown located in the same positions as inthe FIGS. 3-7 embodiment and can be independently exited so that theinteraction of the magnetic field of the permanent magnet and the coilscooperate to produce the appropriate magnetic field to cause movement ofthe mirror portion along each axis 31 and 35, as desired. Although fourair coils are shown, if desired, three air coils could be used toproduce the desired magnetic field.

Although the invention has been described with regards to specificpreferred embodiments thereof, variations and modifications will becomeapparent to those skilled in the art. For example, magnet and air coillocations other than those described above can be employed as long asappropriate currents can be applied by means of control 100 to the aircoils to move the gimbaled mirror to a desired orientation. In thisrespect, with reference to the four coil arrangement shown, a push-pulldrive in control 100 is preferred. Further, although permanent magnetsare shown attached to the movable mirror assembly, it will beappreciated that, if desired, magnetic material could be added to theassembly instead of the permanent magnets and polarized perpendicular tothe mirror surface. It is therefore the intention that the appendedclaims be interpreted as broadly as possible in view of the prior art toinclude all such variations and modifications.

1.-10. (canceled)
 11. A method for use in operating an optical beamswitching system for transmitting an optical beam from at least onesource to at least one of a plurality of optical receptors, said methodcomprising the steps of: providing one or more beam directing devices inan optical pathway of said optical beam, said beam-directing devicesbeing operative for selectively redirecting said optical beam; obtaininginformation from at least one feedback device, indicating an actual beamredirection position associated with at least one of said beam directingdevices; and selectively repositioning said at least one of said beamdirecting devices based on said information.
 12. A method according toclaim 11, wherein said step of obtaining information comprises disposingsaid at least one feedback device adjacent to at least one of the beamdirecting devices.
 13. A method according to claim 11, wherein said stepof obtaining information comprises disposing said at least one feedbackdevice adjacent to at least one of the optical receptors.
 14. A methodaccording to claim 11, wherein at least one of said beam-directingdevices is a movable mirror.
 15. A method according to claim 14, whereinsaid step of repositioning comprises moving the movable mirror about atleast one axis of rotation.
 16. A method as set forth in claim 11,wherein said step of obtaining information comprises obtaining saidinformation from a radiation emitter device.
 17. A method as set forthin claim 11, wherein said step of obtaining information comprisesobtaining said information from a servo control element.
 18. A method asset forth in claim 11, wherein said step of obtaining informationcomprises obtaining said information from a data gathering andtransmission element.
 19. A method as set forth in claim 11, whereinsaid step of providing comprises providing at least one first beamdirecting device and at least one second beam directing device, said atleast one first beam directing device being operative for redirectingsaid optical beam between said at least one source and said at least onesecond beam directing device and said at least one second beam directingdevice being operative for redirecting said optical beam between said atleast one first beam directing device and said at least one of aplurality of optical receptors.
 20. A method as set forth in claim 19,wherein said step of providing further comprises providing at least oneadditional beam directing device operative for redirecting said opticalbeam between said at least one first beam directing device and said atleast one second beam directing device.
 21. A method for use inoperating an optical beam switching system for transmitting an opticalbeam from at least one source to at least one of a plurality of opticalreceptors, said method comprising the steps of: providing one or morebeam directing devices in an optical pathway of said optical beam, saidbeam-directing devices being operative for selectively redirecting saidoptical beam; obtaining information from a feedback device, indicatingan actual beam redirection position associated with at least one of saidbeam directing devices; performing a comparison of the actual beamredirection position with a desired beam-redirection position; andselectively repositioning the first beam-directing device based on thecomparison.
 22. A method according to claim 21, wherein said step ofobtaining information comprises disposing at least one radiation emitteradjacent to at least one of the beam directing devices.
 23. A methodaccording to claim 21, wherein said step of obtaining informationcomprises disposing at least one radiation emitter adjacent to at leastone of the optical receptors.
 24. A method according to claim 21,wherein at least one of said beam-directing devices is a movable mirror.25. A method according to claim 24, wherein said step of repositioningcomprises moving the movable mirror about at least one axis of rotation.26. A method as set forth in claim 21, wherein said step of obtaininginformation comprises obtaining said information from a radiationemitter device.
 27. A method as set forth in claim 21, wherein said stepof obtaining information comprises obtaining said information from aservo control element.
 28. A method as set forth in claim 21, whereinsaid step of obtaining information comprises obtaining said informationfrom a data gathering and transmission element.
 29. A method as setforth in claim 21, wherein said step of providing comprises providing atleast one first beam directing device and at least one second beamdirecting device, said at least one first beam directing device beingoperative for redirecting said optical beam between said at least onesource and said at least one second beam directing device and said atleast one second beam directing device being operative for redirectingsaid optical beam between said at least one first beam directing deviceand said at least one of a plurality of optical receptors.
 30. A methodas set forth in claim 29, wherein said step of providing furthercomprises providing at least one additional beam directing deviceoperative for redirecting said optical beam between said at least onefirst beam directing device and said at least one second beam directingdevice.